A main driving force in the development of wireless/cellular communication networks and systems is to provide, apart from many other aspects, increased coverage or support of higher data rate, or a combination of both. At the same time, the cost aspect of building and maintaining the system is of great importance and is expected to become even more so in the future. As data rates and/or communication distances are increased, the problem of increased battery consumption is another area of concern.
Until recently the main topology of wireless networks has been fairly unchanged, including the three existing generations of cellular networks. The topology is characterized by the cellular architecture with fixed radio base stations (BS) and mobile stations (MS) as the (wireless) transmitting and receiving entities in the networks, wherein a communication typically only involves these two entities.
Attention has recently been given to other types of topologies utilizing relaying to enhance the performance of the system. In its simplest form, a relay system can be seen as a relay station (RS) positioned in-between the base station and the mobile station that repeats and amplify the transmissions in both directions. A slightly more advanced relaying scheme demodulate and decode its received signals prior re-encoding and re-modulating the signal prior forwarding it to the next station.
This, for example, increases the coverage of the base station. Even more elaborate relaying systems, for example systems utilizing cooperative relaying, as described in WO04107693, may give substantially improved performance with regards to throughput, power efficiency and/or capacity. In cooperative relaying, typically a plurality of in parallel operating relay stations are engaged in the communication between the two end nodes, for example a base station and a mobile station.
A related approach to a relay oriented communication systems are exemplified by multihop, or ad-hoc, networks, wherein typically, in a wireless scenario, a communication involves a plurality of transmitting and receiving entities forwarding information towards one or more destination station. Such systems offer possibilities of significantly reduced path loss between communicating (relay) stations that may benefit the end-to-end (ETE) users. Although different in many aspects, the relay enhanced cellular systems and the multihop systems share the concept of relaying information in at least two hops between the end-to-end users.
In classical communication between nodes utilizing relaying, transmissions from the relay station generally operates by sending data packets to different nodes over orthogonal resources, such as consecutive timeslots. The basic prior-art scheme for communication over a relay station can be seen as a four-phase protocol as shown in FIG. 1a, wherein (1) to (4) represent different time instances. The end nodes v1 and v2, for example a base station 105 and a mobile station 110, are engaged in bidirectional communication via a third node v3, a relay station 115. At the first phase (1) the base station 105 transmit a signal S1 to the relay station 115, which in the second phase (2), transmit the received signal S1 to the mobile station 110. In the same manner the relay station 115 transmit a signal S2 in the other direction. that it received from mobile station 110 in the third phase and that it transmits to base station 105 in the fourth (4) phase. The order of the four phases is exemplary and could be, to some extent, interchanged. The transmission performed by the relay station 115 may be a simple amplification and forwarding, or alternatively the signal may be decoded, re-modulated and forwarded. The former is known as amplify-and-forward, or non-regenerative relaying whereas the latter is known as decode-and-forward or regenerative relaying. Both regenerative and non-regenerative relaying is well known, e.g. in traditional multihopping and repeater solutions respectively. Various aspects of the two approaches are addressed in WO04107693. Regardless of if the transmission is regenerative or non-regenerative the traditional relaying concepts comprises at least four separate transmissions for bi-directional traffic.
Improvements to the traditional relaying protocol requiring four phases have been disclosed in U.S. Pat. No. 5,596,439. This method utilizes a priori known information of transmitting stations to enhance throughput. More precisely, U.S. Pat. No. 5,596,439 teaches a method of analogue and linear interference cancellation of a priori known own generated information in a bi-directional three-node satellite communication network. The concept, as illustrated in FIG. 1b, involves two nodes exchanging information through an intermediate relay station. The first node v1 105 transmit a first signal S1 and stores its own transmitted signal S1 (1). The second node v2 110 transmits and stores its signal S2 (2). The intermediate node v3, the relaying node 115, having received both signals, concurrently transmit signals S1 and S2 to both the first and second nodes v1 and v2 (3). With the use of their respective a priori known information, the own transmitted signal, the first node will, prior to demodulation, cancel S1 to extract S2 and the second node will, prior to demodulation, cancel S2 to extract S1. In this way the first node may properly decode S2 and the second node S1, with a reduced number of transmissions compared to the traditional relaying protocol. If the first transmissions from the first and second nodes are concurrent, the intermediate node v3 115 may receive superimposed signals from both nodes prior to relaying it. As both nodes can receive the superimposed signal they may subtract the interference caused by the a priori known signal by properly adjusting phase, delay and amplitudes for the cancellation. Thereby a protocol with only two phases is suggested.
The methods and arrangement described in the document mentioned above introduce improvements as compared to the traditional four-step scheme. However, the a priori information is in the prior art not utilized in an optimal way and further gains in transmitted power and/or increased throughput is needed to meet the growing demands of increased coverage and data rates, for example.